The present invention relates to an aqueous curing composition of a fluoroelastomer and an article coated with a fluoroelastomer. In particular, the present invention relates an aqueous curing composition of a fluoroelastomer containing a specific surfactant, and an article coated with a coating film formed from such a composition.
Fluoroelastomer coating compositions are widely used as industrial materials with being coated on or impregnated in fabric, fibers, metals, plastics, rubbers and other various substrates by making use of good heat resistance, weather resistance, oil resistance, solvent resistance and chemical resistance of the fluoroelastomers. In these years, particularly, aqueous coating compositions are increasingly used since they are friendly to the environments.
The conventional aqueous composition of fluoroelastomers usually contain a polyoxyethylene alkylphenyl ether of the formula:
Rxe2x80x94Phxe2x80x94O(CH2CH2O)nH
wherein R is an alkyl group, Ph is a phenylene group and n is an integer of at, least 1 as a surfactant.
However, this type of the surfactant tends to leave decomposition residues in the coating film of the fluoroelastomer after baking, since it has a relatively high decomposition temperature, and thus it may deteriorate the above-described inherent characteristics of the fluoroelastomer. When such a surfactant is used in a coating film covering the surface of a roll used in office automation equipment (e.g. copying machines, printers, etc.), the coating film has insufficient durability.
This type of the surfactant is not preferable from the viewpoint of environmental protection, since it is prepared from a raw material which is suspected to have internal secretion disturbing functions.
One object of the present invention is to provide an aqueous curing composition of a fluoroelastomer, which can make use of the inherent characteristics of the fluoroelastomer coating.
Another object of the present invention is to provide an article coated with a fluoroelastomer, which can solve the above drawbacks of the articles coated with a film formed from the conventional aqueous curing composition of a fluoroelastomer, in particular, the rolls of the office automation equipment.
The above objects can be achieved by an aqueous curing composition of a fluoroelastomer comprising a fluoroelastomer, a curing agent, and a surfactant with which an amount of decomposition residues is 0.3% by weight or less after being baked at 300xc2x0 C. for 30 minutes, and an article at least a part of the surface of which is coated with a coating film formed from such an aqueous curing composition of a fluoroelastomer.
Hereinafter, the components contained in the composition of the present invention will be explained.
The fluoroelastomer is usually supplied in the form of an aqueous dispersion. The aqueous dispersion of the fluoroelastomer is prepared by dispersing a fluorine-containing elastomeric copolymer (fluoroelastomer) in water at a concentration of 10 to 75% by weight in the presence of a surfactant.
The fluorine-containing elastomeric copolymer is a fluorine-containing copolymer containing repeating units represented by xe2x80x94CH2xe2x80x94 in the backbones. One typical example of such a copolymer is a fluorine-containing elastic copolymer comprising vinylidene fluoride. Examples of such copolymer are copolymers comprising at least one repeating unit selected from the group consisting of xe2x80x94CF2xe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94 and xe2x80x94CH2xe2x80x94CH(CH3)xe2x80x94, and at least one repeating unit selected from the group consisting of xe2x80x94CF2xe2x80x94CF(CF3)xe2x80x94, xe2x80x94CF2xe2x80x94CF2xe2x80x94 and xe2x80x94CF2xe2x80x94CF(ORf)xe2x80x94 in which Rf is a fluoroalkyl group having 1 to 6 carbon atoms.
Specific examples of such copolymers include vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers, ethylene-hexafluoropropylene copolymers, tetrafluoroethylene-propylene copolymers, etc. Among them, the vinylidene fluoride copolymers are preferable from the viewpoint of their crosslinkability.
Such fluorine-containing elastomeric copolymers are commercially distributed under the trade name of xe2x80x9cDAIEL(copyright)xe2x80x9d (available from Daikin Industries, Ltd.), xe2x80x9cVITONE FLOME(copyright)xe2x80x9d (available from E. I. duPont), xe2x80x9cAFLAS(copyright)xe2x80x9d (available from ASAHI GLASS Co., Ltd.), etc.
The amount of the fluoroelastomer (solid component) to be contained in the composition of the present invention is from 1 to 500 parts by weight, preferably from 5 to 300 parts by weight, more preferably from 10 to 150 parts by weight, per 100 parts by weight of water.
The curing agent to be contained in the aqueous curing composition of the present invention may be either a conventional diamine curing agent or a conventional polyol curing agent.
Examples of the diamine curing agent include an aminosilane compound of the formula: 
wherein R1 is a methyl group or an ethyl group, Z is a single bond, xe2x80x94C2H4NHxe2x80x94, xe2x80x94CONHxe2x80x94 or xe2x80x94C2H4NHxe2x80x94C2H4NHxe2x80x94NHxe2x80x94, and y is 2 or 3, or its partially or completely hydrolyzed products, and a polyaminosiloxane compound of the formula: 
wherein R2, R3 and R4 represent independently of each other a hydrogen atom, an alkyl group having 1 to 6 carbon atom, an amino group, a polyamino group, or an alkyl group having 1 to 6 carbon group at least one hydrogen atom of which is replaced with an amino group or a polyamino group provided that the amino groups are present in at least two of R2, R3 and R4 or a polyamino group is present in at least one of R2, R3 and R4.
The polyol curing agent used in the present invention may be a compound or a polymer having at least two hydroxyl groups, in particular, phenolic hydroxyl groups in a molecule, and having a curing capability. Specific examples of polyol curing agents include salts of basic compounds with phenol compounds such as 
and polyphenols represented by the formula: 
wherein Y is a hydrogen atom, a halogen atom, R5, xe2x80x94CH2OR5 or xe2x80x94OR5, Z is xe2x80x94CH2xe2x80x94 or xe2x80x94CH2OCH2xe2x80x94, R5 is an alkyl group having 1 to 4 carbon atoms, and n is an integer of 0 to 100.
Examples of the basic compounds include ammonium salts, tertiary amines, phosphonium salts, alkali metals and alkaline earth metals.
Specific examples of ammonium salts include trimethylbenzylammonium, triethylbenzylammonium, dimethyldecylbenzylammonium, triethylbenzylammonium, myristylbenzyldimethylammonium, dodecyltrimethylammonium, dimethyltetradecylbenzylammonium, trimethyltetradecylammonium, coconuttrimethylammonium, stearyltrimethylammonium, distearyldimethylammonium, tetrabutylammonium, 1,4-phenylenedimethylenebistrimethylammonium, 1,4-phenylenedimethylenebistriethylammonium, ethylenebistriethylammonium, etc.
Specific examples of tertiary amines include 1,8-diaza-bicyclo[5.4.0]-undecene-7, 8-methyl-1,8-diaza-bicyclo[5.4.0]-undecene-7, 8-propyl-1,8-diazabicyclo[5.4.0]-undecene-7, 8-dodecyl-1,8-diaza-bicyclo[5.4.0]-undecene-7, 8-eicocyl-1,8-diaza-bicyclo[5.4.0]-undecene-7, 8-tetracocyl-1,8-diaza-bicyclo[5.4.0]-undecene-7, 8-benzyl-1,8-diaza-bicyclo[5.4.0]-undecene-7, 8-phenethyl-1,8-diazabicyclo-[5.4.0]-undecene-7, 8-(3-phenylpropyl)-1,8-diaza-bicyclo[5.4.0]-undecene-7, trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, triisobutylamine, methyldiethylamine, dimethylethylamine, dimethyl-n-propylamine, dimethyl-n-butylamine, dimethylisobutylamine, dimethylisopropylamine, dimethyl-sec.-butylamine, dimethyl-tert.-butylamine, triallylamine, diallylmethylamine, allyldimethylamine, benzyldimethylamine, benzyldiethylamine, N-allylpiperidine, N-ethylpiperidine, N-butylpiperidine, N-methylpyrolidine, N-cyclohexylpyrolidine, N-n-butylpyrolidine, N-ethylpyrolidine, N-benzylpyrolidine, 2,4,6-trimethylpyridine, etc.
Specific examples of phosphonium salts include benzyltriphenylphosphonium, methyltriphenylphosphonium, 2,4-dichlorobenzyltriphenylphosphonium, 4-methylbenzyltriphenylphosphonium, 4-chlorobenzyltriphenylphosphonium, m-trifluoromethylbenzyltriphenylphosphonium, 2-cyanobenzyltriphenylphosphonium, xcex1-carbethoxybenzyltriphenylphosphonium, diphenylmethyltriphenylphosphonium, 1-naphthylmethyltriphenylphosphonium, carbethoxymethyltriphenylphosphonium, methoxymethyltriphenylphosphonium, allyloxymethyltriphenylphosphonium, 1-carbethoxyethyltriphenylphosphonium, isobutyltriphenylphosphonium, 4-cyanobutyltriphenylphosphonium, 2-pentyltriphenylphosphonium, allyltriphenylphosphonium, tetraphenylphosphonium, methyltrioctylphosphonium, benzyltrioctylphosphonium, methoxyethoxyethyltrioctylphosphonium, butyltrioctylphosphonium, m-trifluoromethylbenzyltrioctylphosphonium, 2,2,3,3-tetrafluoropropyltrioctylphosphonium, 2,2,3,3,4,4,5,5-octafluoropentyltrioctylphosphonium, tetraoctylphosphonium, tetrabutylphosphonium, etc.
Specific examples of alkali metals are lithium, sodium, potassium, etc.
Specific examples of alkaline earth metals are beryllium, magnesium, calcium, barium, etc.
Among them, the salts of hydroquinone, bisphenol A, bisphenol AF or the resol type polyphenols with ammonium salts or tertiary amines are preferable from the viewpoint of the properties of the coating film. Hydroquinone, bisphenol A, bisphenol AF and the resol type polyphenols have excellent curing properties, and the ammonium salts and the tertiary amines do not leave the decomposition residues in the coating film unlike the alkali metals or the alkaline earth metals.
When the polyol curing agent is used, the following compounds may be compounded as the optional curing accelerators:
A quaternary ammonium salt of the formula:
NR64X or R63Nxe2x80x94R7xe2x80x94NR63.2X
wherein R6 groups are the same or different and represent an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms, provided that two or more of R6 groups may together form a carbocyclic group or a heterocyclic group; R7 is an alkylene group having 2 to 21 carbon atom or a phenylenedialkylene group having 8 to 12 carbon atoms; and X is an acid radical or a hydroxyl group.
Examples of acid radicals include halides, sulfate, sulfite, bisulfite, thiosulfate, sulfide, polysulfide, hydrogen sulfide, thiocyanate, carbonate, bicarbonate, nitrate, carboxylate, borate, phosphate, biphosphate, phosphite, perchlorate, bifluoride, arsenate, ferricyanide, ferrocyanide, molybdate, selenate, selenite, uranate, tungstate, etc.
Specific examples of the quaternary ammonium salts include alkyl and aralkyl quaternary ammonium salts (e.g. trimethylbenzylammonium chloride, triethylbenzylammonium chloride, dimethyldecyibenzylammonium chloride, triethylbenzylammonium chloride, myristylbenzyldimethylammonium chloride, dodecyltrimethylammonium chloride, dimethyltetradecylbenzylammonium chloride, trimethyltetradecylammonium chloride, coconuttrimethylammonium chloride, stearyltrimethylammonium chloride, distearyldimethylammonium chloride, tetrabutylammonium hydroxide, 1,4-phenylenedimethylene-bistrimethylammonium dichloride, 1,4-phenylenedimethylene-bistriethylammonium dichloride, ethylenebistriethylammonium dibromide, etc.), and quaternary 1,8-diaza-bicyclo[5.4.0]-7-undecenium salts (e.g. 8-methyl-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, 8-methyl-1,8-diaza-bicylo[5.4.0]-7-undecenium iodide, 8-methyl-1,8-diaza-bicylo[5.4.0]-7-undecenium hydroxide, 8-methyl-1,8-diaza-bicylo[5.4.0]-7-undecenium methylsulfate, 8-methyl-1,8-diaza-bicylo[5.4.0]-7-undecenium bromide, 8-propyl-1,8-diaza-bicylo[5.4.0]-7-undecenium bromide, 8-dodecyl-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, 8-dodecyl-1,8-diaza-bicylo[5.4.0]-7-undecenium hydroxide, 8-eicosyl-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, 8-tetracosyl-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, 8-benzyl-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, 8-benzyl-1,8-diaza-bicylo[5.4.0]-7-undecenium hydroxide, 8-phenethyl-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, 8-(3-phenylpropyl)-1,8-diaza-bicylo[5.4.0]-7-undecenium chloride, etc.).
NR63 or R62Nxe2x80x94R7xe2x80x94NR62
wherein R6 and R7 are the same as defined above.
Specific examples of the tertiary amines include trimethylamine, triethylamine, tri-n-propylamine, tri-n-butylamine, triisobutylamine, methyldiethylamine, dimethylethylamine, dimethyl-n-propylamine, dimethyl-n-butylamine, dimethylisobutylamine, dimethylisopropylamine, dimethyl-sec.-butylamine, dimethyl-tert.-butylamine, triallylamine, diallylmethylamine, allyldimethylamine, benzyldimethylamine, benzyldiethylamine, N-allylpiperidine, N-ethylpiperidine, N-butylpiperidine, N-methylpyrolidine, N-cyclohexylpyrolidine, N-n-butylpyrolidine, N-ethylpyrolidine, N-benzylpyrolidine, 2,4,6-trimethylpyridine, etc.
Examples of the inorganic or organic acids which form the quaternary salts include the following acids:
HCl, HBr, HF, (C2H5)3NH+Clxe2x88x92, (C2H5)3NH+NO3xe2x88x92, 2(C2H5)3NH+SO42xe2x88x92, 2(C2H5)3NH+CO32xe2x88x92, (C2H5)3NH+R8Oxe2x88x92, (C2H5)3NH+R8COOxe2x88x92, (C4H9)3NH+Clxe2x88x92, (C4H9)3NH+NO3xe2x88x92, 2(C4H9)3NH+SO42xe2x88x92, 2(C4H9)3NH+CO32xe2x88x92, (C4H9)3NH+R8Oxe2x88x92, (C4H9)3NH+R8COOxe2x88x92 wherein R8 is an alkyl or alkenyl group having 1 to 20 carbon atoms or an aryl group having 6 to 20 carbon atoms.
Primary and secondary amines are less preferable since they may induce reactions other than the polyol curing.
A quaternary phosphonium salt of the formula:
PR64X or R63Pxe2x80x94R7xe2x80x94PR63.2X
wherein R6, R7 and X are the same as defined above.
Examples of the phosphonium salts include benzyltriphenylphosphonium chloride, benzyltriphenylphosphonium bromide, methyltriphenylphosphonium methylmethanephosphonate, bis(benzyldiphenylphosphin)iminium chloride, 2,4-dichlorobenzyltriphenylphosphonium chloride, 4-methylbenzyltriphenylphosphonium chloride, 4-chlorobenzyltriphenylphosphonium chloride, m-trifluoromethylbenzylriphenylphosphonium chloride, 2-cyanobenzyltriphenylhosphonium bromide, xcex1-carbethoxybenzyltriphenylphosphonium bromide, diphenylmethyltriphenylphosphonium chloride, 1-naphthylmethyltriphenylphosphonium chloride, carbethoxymethyltriphenylphosphonium bromide, methoxymethyltriphenylphosphonium chloride, allyloxymethyltriphenylphosphonium chloride, 1-carbethoxyethyltriphenylphosphonium chloride, isobutyltriphenylphosphonium bromide, 4-cyanobutyltriphenylphosphonium bromide, 2-pentyltriphenylphosphonium bromide, allyltriphenylphosphonium chloride, tetraphenylphosphonium chloride, tetraphenylphosphonium bromide, methyltrioctylphosphonium chloride, methyltrioctylphosphonium tetrafluoroborate, methyltrioctylphosphonium acetate, methyltrioctylphosphonium dimethylphosphate, benzyltrioctylphosphonium chloride, benzyltrioctylphosphonium bromide, methoxyethoxyethyltrioctylphosphonium chloride, butyltrioctylphosphonium bromide, m-trifluoromethylbenzyltrioctylphosphonium chloride, 2,2,3,3-tetrafluoropropyltrioctylphosphonium chloride, 2,2,3,3,4,4,5,5-octafluoropentyltrioctylphosphonium chloride, tetraoctylphosphonium bromide, tetrabutylphosphonium chloride, etc.
In the present invention, organic acids can be added to the composition to improve the storage stability of the composition. Organic acids having 1 to 12 carbon atoms, preferably 1 to 4 carbon atoms are used. Organic acids having 13 or more carbon atoms are less preferable, since they remain in the coating films. Preferable examples of the organic acids are monocarboxylic acids such as formic acid, acetic acid, propionic acid, etc.; and dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, etc.
The organic acids suppress the polyol curing of the fluorine-containing copolymers in the compositions during storage. However, the organic acids evaporate or decompose when the compositions are applied, dried and baked, and then the basic compound can accelerate the curing reaction. Thus, the organic acid is included in the xe2x80x9ccuring acceleratorsxe2x80x9d according to the present invention.
The composition of the present invention contains 0.01 to 50 parts by weight, preferably 0.1 to 20 parts by weight of the amine curing agent, per 100 parts by weight of the fluoroelastomer in the case of the diamine curing, or the composition contains 0.1 to 20 parts by weight, preferably 1 to 10 parts by weight of the polyol curing agent, and 0 to 10 parts by weight, preferably 0.01 to 5 parts by weight of the curing accelerator, per 100 parts by weight of the fluoroelastomer in the case of the polyol curing. When the amount of the curing accelerator is less than the above lower limit, the curing may not proceed. When the amount of the curing accelerator exceeds the above upper limit, it may be difficult to control the curing reaction.
Ionic surfactants and nonionic surfactants may be used as surfactants to disperse the fluoroelastomer and various additives in water, but they should be decomposed at a relatively low temperature. That is, in the present invention, the surfactant should leave 0.3% by weight or less, preferably 0.25% by weight or less, more preferably 0.1% by weight or less of a decomposition residue after being heated at 300xc2x0 C. for 30 minutes.
Examples of such surfactants include nonionic surfactants having no phenyl group such as a polyoxyethylene alkyl ether of the formula:
R9xe2x80x94O(CH2CH2O)nH
wherein R9 is an alkyl group, preferably an alkyl group having 1 to 20 carbon atoms, and n is a number of at least 1 (one), preferably up to 30, more preferably up to 20, and a polyoxyethylenepolyoxypropylene block copolymer of the formula:
H(CH2CH2O)mxe2x80x94[CH2CH(CH3)O]kxe2x80x94(CH2CH2O)mxe2x80x2H
wherein m, mxe2x80x2 and k are each a number of at least 1 provided that the sum of m, mxe2x80x2 and k is preferably no more than 1,000, more preferably no more than 500.
These surfactants are preferable from the viewpoint of environment protection, since they are prepared without using any chemical material that is doubtful if it may have internal secretion disturbing functions as a raw material, and they are synthesized from internal secretion non-disturbing materials.
The surfactant, which leaves 0.3% by mole or less of the decomposition residue after being heated at 300xc2x0 C. for 30 minutes, is added to the composition in an amount of 1 to 100 parts by weight, preferably 10 to 50 parts by weight, per 100 parts by weight of the fluoroelastomer.
The composition of the present invention may contain various additives which are added to conventional fluoroelastomer compositions, for example, fillers, colorants, acid-acceptors, and the like, in addition to the above components.
Examples of the fillers are carbon black, white carbon, calcium carbonate, barium sulfate, etc., and examples of the colorants are inorganic pigments, compound oxide pigments, etc.
Examples of the acid-acceptors are magnesium oxide, lead oxide, zinc oxide, lead carbonate, zinc carbonate, double salts such as hydrotalcite, etc. Compounds having a high activity such as calcium hydroxide are less preferred, since they tend to cause gelation. Preferably, the acid-acceptors have a smaller pKa than that of the above basic compounds. When the pKa of acid-acceptors is high, the compositions of the present invention tend to be gelled.
In general, the acid-acceptor is compounded in an amount of from 1 to 40 parts by weight per 100 parts by weight of a fluorine-containing copolymer, depending on its activity.
The compositions of the present invention may be applied and cured by the same methods as those for applying and curing the conventional aqueous curing composition of the fluoroelastomer.
For example, the compositions are applied to an article to be coated by brush coating, spray coating, dip coating, flow coating, dispenser coating, screen coating, etc. according to the properties of the compositions, and thoroughly dried. Then, the compositions coated are baked at a temperature of from 150 to 300xc2x0 C. for 10 to 120 minutes.
Furthermore, a surface layer may be formed on the coating film formed from the composition of the present invention. The surface layer may be formed from a fluororesin and/or a terminal-modified perfluoropolyether by a conventional method.
Examples of the fluororesin include polyvinylidene fluoride (PVdF), ethylene-tetrafluoroethylene copolymers (ETFE), polychlorotrifluoroethylene (PCTFE), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymers (EPA), tetrafluoroethylene-hexafluoro-propylene copolymers (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers (PFA), polytetra-fluoroethylene (PTFE), terminal-modified EPA, terminal-modified FEP, terminal-modified PFA, etc. Among them, tetrafluoroethylene base polymers are preferable from the viewpoint of the non-stickiness.
The terminal-modified perfluoropolyether to be used in the present invention comprises at least one repeating unit selected from the group consisting of xe2x80x94[CF(CF3)xe2x80x94CF2O]xe2x80x94, xe2x80x94(CF2O)xe2x80x94, xe2x80x94(CF2CF2O)xe2x80x94 and xe2x80x94(CF2CF2CF2O)xe2x80x94 in its backbone. The total number of the repeating units is from 1 to 1,000.
Examples of functional groups which modify the molecular terminals of the perfluoropolyether include Cl, Br, I, NR10R11 wherein R10 and R11 are independently of each other and represent a hydrogen atom, an aryl group, a C1-C10 alkyl group or a C3-C10 cycloalkyl group, SH, NCO, NO2, COOH, PO2H, SO3H, OH, a glycidyl group or a hydroxyphenyl group. The functional groups may be present at the terminals of the backbone or the terminal of side chains of the perfluoropolyether.
These functional groups may be directly bonded to the backbone consisting of the above repeating units of the perfluoropolyether, or through a group of the formula: xe2x80x94(CH2)nxe2x80x94, xe2x80x94(CF2)nxe2x80x94, xe2x80x94(CH2O)nxe2x80x94 or xe2x80x94(CF2O)nxe2x80x94 in which n is a number of 1 to 100.
The surface of an article to be coated is preferably well degreased and cleaned prior to the application of the composition of the present invention.
It is preferable to form a primer layer on the surface of the article with silane primers, silicone primers, etc. to increase the adhesion between the article and the composition.
Examples of the articles to be coated with the composition of the present invention include metals (e.g. iron, stainless steel, copper, aluminum, brass, etc.), glass products (e.g. such as glass plates, fabric or non-woven fabric of glass fiber, etc.), molded articles and coated articles of general or heat-resistant resins (e.g. polypropylene, polyoxymethylene, polyimide, polyamideimide, polysulfone, polyethersulfone, polyetheretherketone, etc.), molded articles and coated articles of general rubbers (e.g. styrene-butadiene rubber (SBR), butyl rubber, nitrile rubber (NBR), ethylene-propylene rubber (EPDM), etc.) and heat-resistant rubbers (e.g. silicone rubber, fluoroelastomer, etc.), fabric or non-woven fabric of natural and synthetic fibers, and the like.
The articles coated with the film formed from the composition of the present invention can be used in various fields which require heat resistance, solvent resistance, lubrication and/or non-stick properties. Specific examples of the applications include rolls (e.g. fixing rolls, press rolls, etc.) and conveying belts for OA equipment such as copying machines, printers, facsimiles, etc.; sheetsandbelts; O-rings, diaphragms, chemical-resistant tubes, fuel hoses, valve seals, gaskets for chemical plants, engine gaskets, and the like.